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264

WHITE  METAL

(b) Determination of ths antimony. The antimony sulphide on the
filter (see i) is dissolved in a little yellow ammonium sulphide, the solution
evaporated in a tared porcelain crucible, the residue treated carefully, to
avoid spurting, with nitric acid and the liquid evaporated to dryness. The
treatment with nitric acid is repeated twice to ensure the complete oxidation
of the sulphur, the residue being ignited and weighed : Sb204 x 07898 =
Sb.

2. DETERMINATION OF THE LEAD, COPPER, IRON AND ZINC. The sul-
phides remaining undissolved in sodium sulphide are dissolved in nitric
acid (D 1-2), the filtered solution treated with a little sulphuric acid and
evaporated until white fumes appear, the subsequent procedure being as
indicated for the gravimetric determination of lead, copper, iron and zinc
in ordinary brass.

2. Alloys with a Lead-Antimony-Tin Basis

These alloys usually contain 60-80% Pb, 10-15% Sb, 10-25% Sn, a
little copper and possibly zinc, iron, arsenic. The complete analysis is
carried out as follows :

A.  Electrolytically.—i gram of the sample in fine filings is treated
with 20 c.c. of cone, hydrochloric acid and 2-3 c.c. of cone, nitric acid and
left overnight in order that the action may proceed slowly but completely.

1.  DETERMINATION OF THE LEAD.    The acid solution is treated with
10 vols. of absolute alcohol (220-230 c.c.), cooled and after a suitable rest
(3-4 hours)—when the bulk of the lead chloride has separated (only a few
milligrams, to be estimated later, remain in solution)—filtered through a
tared Gooch crucible, washed with alcohol to a neutral reaction, dried at
100° and weighed:   PbCl2 x 0-7447 = Pb.

2.  DETERMINATION OF THE TIN, ANTIMONY, COPPER, IRON AND ZINC.
The alcoholic solution, freed from lead chloride, is evaporated with 2-3
grams of tartaric acid until the alcohol is completely expelled, then made
slightly alkaline with concentrated sodium hydroxide solution and treated
with 2 grams of sodium hydroxide and 15-20 c.c. of sodium sulphide solu-
tion (D = i'225).   After being heated for about 15 minutes on a water-
bath, the liquid is filtered into a Classen capsule, the precipitate being
washed five or six times with sodium sulphide solution (60-70 c.c.  in all)
and then with hot water containing a few drops Of sodium sulphide.    The
filtrate contains the tin and antimony and the insoluble residue the copper,
traces of lead dissolved as chloride, and any iron and zinc present.

For the electrolytic determination of these elements, the method pre-
viously described (see i,A, p. 261) 1 is followed.

B.  Gravimetrically.

i. DETERMINATION OF THE LEAD, i gram of the sample is attacked
with aqua regia and the lead separated as chloride under the conditions
described above (see A}.

1 If the copper is present in very small amount, it is more convenient to make
the direct determination (see p. 261) and in such case, when the lead in solution as
chloride is to be determined, it is advisable to add a little copper nitrate to the electrolyte.d off and washed with hydrogen sulphide